Optical channel plates with optical fibers or hollow waveguides

ABSTRACT

A method of forming a solid or honeycombed optical channel plate, having solid or hollow waveguides respectively, from aligned optical waveguides. Reflective optical channel plates are also disclosed for use with a front projection screen and transmission optical channel plates are also disclosed for use with a front projection screen and transmission optical channel plates for use with a rear projection screen for increasing luminance and/or resolution of an image projected on the screen.

[0001] This invention relates to reflection and transmission opticalchannel plates, in particular for use with display devices.

[0002] The use of optical channel plates, or face plates, in associationwith display devices is known. For example, U.S. Pat. No. 5,911,024discloses a fibre optic display constructed from a plurality of shortoptical fibres whereby an enlarged image can be produced from a cathoderay tube. Similarly a front fibre optic face plate for use in a liquidcrystal display has been disclosed in, for example, U.S. Pat. No.5,959,711.

[0003] One application of the present invention is for front projectionscreens. The flat surface of known front projection screens is notshielded from stray light and reflections of the stray light from thescreen can degrade an image projected on the screen. Moreover, lightincident on the screen is scattered with only a small proportion of theincident light being reflected towards a viewer. In order to seek toovercome this problem, use has been made of metallised fabrics orplastics with some success but only for applications where the screen isviewed from a distance.

[0004] There are also problems with existing rear projection screens,such as those used for large screen televisions, that when viewed atwide angles the image is subject to disturbing colour separation.

[0005] Problems also exist, which are common to front and rearprojection screens, of diffusion of light from a single point on thescreen resulting in a fuzzy image. This contributes to the fact thatonly very small viewing angles can be used for large screens, especiallyfor rear projection screens.

[0006] There are also particular problems with the use of cathode raytube displays. In particular, the tubes have high power consumption andgeometric distortion is introduced by the displays. To overcome thegeometric distortion the displays require further magnetic elements inaddition to cathode ray tube deflecting coils. There is also a possibleproblem of harmful radiation levels from prolonged exposure to cathoderay tubes. Although liquid crystal displays potentially would overcomemany of these problems, liquid crystal displays suffer even more thancathode ray tubes from difficult viewing under strong lightingconditions, particularly due to reflections of stray or ambient lightfrom the screen.

[0007] It is an object of this invention to seek at least partially toameliorate these difficulties.

[0008] It is a particular object of the present invention to provide analternative method for the production of optical channel plates.

[0009] According to a first embodiment of a first aspect of the presentinvention there is provided a method for forming a solid optical channelplate comprising the steps of: a) providing optical fibres withrespective longitudinal axes in side-by-side relationship; b) usingmechanical aligning means to align the optical fibres in a twodimensional array with the respective longitudinal axes substantiallyparallel, to form a substantially regular geometric pattern incross-section; c) adhering the optical fibres together along at least aportion of their longitudinal surfaces; and d) transversely slicing thearray of optical fibres to form at least one optical channel plate.

[0010] Conveniently, the step of providing optical fibres inside-by-side relationship includes heating and pulling the opticalfibres to form tapering fibres.

[0011] Preferably, the step of providing optical fibres in side-by-siderelationship includes the step of coating the optical fibres withcoatings along longitudinal surfaces of the optical fibres to increaseinternal optical reflectivity of the optical fibres.

[0012] Advantageously, the step of coating the optical fibres includescoating by electroplating.

[0013] Advantageously, the step of aligning the optical fibres withmechanical means includes the step of aligning the optical fibres withultrasonic vibrating means.

[0014] Conveniently, the step of adhering the optical fibres includesultrasonically vibrating the optical fibres such that portions of thecoatings of adjacent optical fibres are heated and welded together.

[0015] Alternatively, the step of the adhering the optical fibrescomprises using adhesive.

[0016] Conveniently, the step of transversely slicing the array to format least one optical channel plate includes the further step, afterslicing the array, of polishing at least one of the opposed end surfacesof the optical fibres, which together form opposed end surfaces of theat least one optical channel plate.

[0017] Advantageously, the step of polishing the at least one of theopposed end surfaces of the at least one optical channel plate includescoating one of the end surfaces of the at least one optical channelplate to increase the internal optical reflectivity of the respectiveend surfaces of the at least one optical channel plate, to form at leastone reflective solid optical channel plate.

[0018] Conveniently, the step of providing optical fibres inside-by-side relationship includes providing optical fibres having acircular transverse cross-section.

[0019] Alternatively, the step of providing optical fibres inside-by-side relationship includes providing optical fibres having apolygonal, preferably hexagonal, transverse cross-section.

[0020] According to a second embodiment of the first aspect of thepresent invention, there is provided a method of forming a honeycombedoptical channel plate comprising the steps of, a) providing an array ofaligned coated fibres, the fibres having optically reflective coatingswith a melting point higher than that of the fibres; b) transverselyslicing the array of coated fibres to form at least one plate of coatedfibres; c) heating the at least one plate of coated fibres to melt thefibres to form molten fibre material; and d) removing the molten fibrematerial from the at least one plate of coated fibres to leave theoptically reflective coatings as hollow optical waveguides forming ahoneycombed optical channel plate.

[0021] Conveniently, the step a) of providing an array of aligned coatedfibres includes the steps of providing an array of aligned fibreslongitudinally spaced apart by longitudinal interstitial spaces; andpassing coating solution between the aligned, spaced apart, fibres tofill the interstitial spaces and thereby coat the fibres along theirlengths to form an array of coated fibres having optically reflectivecoatings with a melting point higher than that of the fibres, such thatthe optically reflective coatings cause the fibres to adhere togetheralong their lengths.

[0022] Advantageously, the step of providing an array of aligned, coatedfibres includes the step of aligning the fibres using ultrasonicvibrating means.

[0023] Conveniently, the step of providing an array includes heating andpulling the fibres to formed tapering fibres.

[0024] Advantageously, the fibres are coated by electroplating.

[0025] Conveniently, the step of providing an array of aligned fibresincludes providing fibres having a circular transverse cross-section.

[0026] Alternatively, the step of providing an array of aligned fibresincludes providing fibres having a polygonal, preferably hexagonal,transverse cross-section.

[0027] Conveniently, the step of slicing the array to form at least oneplate includes coating a major face of the at least one plate with anoptically reflective end coating, such that the step of removing themolten fibre material from the at least one plate leaves the opticallyreflective coatings as hollow optical waveguides closed at one end bythe optically reflective end coating, to form a reflective honeycombedoptical channel plate.

[0028] According to a third embodiment of the first aspect of thepresent invention, there is provided a method for forming an opticalchannel plate comprising the steps of: a) providing an array of alignedoptical waveguides interconnected in side-by-side relationship spacedapart by interstitial spaces; b) clamping the optical waveguides inposition with respect to each other to form clamped optical waveguides;c) transversely slicing the array of waveguides to form at least oneclamped optical waveguide plate with interstitial spaces; d) filling theinterstitial spaces in the waveguide plate with optically reflectivecoating material to improve the internal optical reflectivity of thewaveguides and to adhere the waveguides together in the array; and e)unclamping the clamped optical waveguide plate to form an opticalchannel plate.

[0029] Conveniently, the step of providing an array of aligned opticalwaveguides includes using ultrasonic vibrating means to align theoptical waveguides.

[0030] According to a fourth embodiment of the first aspect of theinvention, there is provided a method of forming an optical channelplate comprising substantially parallel hollow optical waveguides, themethod comprising the steps of: a) providing a plurality of corrugatedsheets of optically reflective material; b) stacking the plurality ofcorrugated sheets one upon another to form substantially parallel spacedapart optical waveguides between adjacent stacked sheets; and c)adhering adjacent sheets to each other.

[0031] Conveniently, the step of providing a plurality of corrugatedsheets of optically reflective material includes the step of coatingsheets of non-optically reflective material with an optically reflectivecoating.

[0032] Conveniently, the step of providing a plurality of corrugatedsheets includes the step of forming corrugated sheets from substantiallyplane sheets by using pressing means to deform the substantially planesheets into corrugated sheets while the sheets are in a ductile state.

[0033] Advantageously, the step of adhering adjacent sheets togetherincludes the further step of slicing the adhered sheets into separatechannel plates.

[0034] According to a fifth embodiment of the first aspect of thepresent invention, there is provided a method of forming an opticalchannel plate comprising substantially parallel optical waveguidescomprising the steps of: providing a block of material; and b) machiningthe block to form substantially parallel optical waveguides therein.

[0035] Conveniently, the step of providing a block of material comprisesproviding a block of optically reflective material.

[0036] Advantageously, the step of machining the block includes thefurther step of coating the substantially parallel optical waveguideswith optically reflective material to increase the internal opticalreflectivity of the optical waveguides.

[0037] Advantageously, the step of machining the block to formsubstantially parallel optical waveguides therein comprises formingsolid optical waveguides of the material of the block.

[0038] Alternatively, the step of machining the block to formsubstantially parallel optical waveguides therein comprises forminghollow optical waveguides within the material of the block.

[0039] Conveniently, the step of machining the block to formsubstantially parallel optical waveguides therein comprises machiningunder numerical control.

[0040] According to a second aspect of the present invention, there isprovided a reflective optical channel plate for a front projectionscreen, the optical channel plate comprising a plurality of opticalwaveguides arranged in an array for location substantially perpendicularto a major plane of the screen such that light of a projected imageentering first ends of the optical waveguides is collimated by theoptical waveguides and reflected from opposed second ends of the opticalwaveguides respectively to be viewed after reflection with substantiallyno interference from stray light reflected from the second ends of thewaveguides.

[0041] Conveniently, the optical waveguides are optical fibres.

[0042] Advantageously, the optical fibres are coated along their lengthsto increase internal reflectivity of the optical fibres.

[0043] Conveniently, the optical waveguides are adhered together alongtheir lengths.

[0044] Advantageously, the second ends of the optical fibres are coatedto increase internal reflectivity of the second ends.

[0045] Advantageously, the optical waveguides are hollow opticalwaveguides.

[0046] Conveniently, the array of hollow waveguides has a honeycombstructure in transverse cross-section.

[0047] Conveniently, the optical waveguides have a circular transversecross-section.

[0048] Alternatively, the optical waveguides have a polygonal,preferably hexagonal, transverse cross-section.

[0049] Conveniently, the channel plate is arcuate in a planesubstantially perpendicular to the axes of the optical waveguides suchthat the channel plate forms a collimated convex or concave mirror.

[0050] According to a third aspect of the present invention, there isprovided a transmission optical channel plate for a display screen, theoptical channel plate comprising a plurality of optical waveguides forarrangement in an array substantially perpendicular to a major plane ofthe screen such that light of an image entering first ends of theoptical waveguides is collimated and transmitted from opposed ends ofthe optical waveguides respectively.

[0051] Conveniently, the optical waveguides taper from the screen toproduce a magnified image on the screen and longitudinal axes of thewaveguides are at least partially arcuate such that light may enter endsof the waveguides at an angle substantially within the plane the screento form a substantially flat display device.

[0052] Advantageously, the optical waveguides trifurcate into threeoptically connected sub-waveguides respectively such that light ofdifferent colours entering from each of the sub-waveguides respectivelymay be combined in each of the waveguides to illuminate a pixel on thescreen, respectively.

[0053] Alternatively, the inner longitudinal surfaces of the waveguidesare coated with photoelectric material, for the emission of electrons.

[0054] Advantageously, the axes of the optical waveguides are arcuate toincrease the number of optical reflections from the coated innerlongitudinal surfaces.

[0055] Embodiments of the invention will now be described by way ofexamples with reference to the accompanying drawings, in which:

[0056] FIGS. 1 to 3 are cross-sectional views of portions of opticalchannel plates according to the present invention having opticalwaveguides of hexagonal, circular and triangular cross-sections,respectively;

[0057]FIG. 4 is a perspective view of a portion of the optical channelplate of FIG. 1;

[0058]FIG. 5 is a perspective view of a portion of the optical channelplate of FIG. 2;

[0059]FIG. 6 is a perspective view of a means of aligning the opticalfibres of the optical channel plate of FIG. 2, using ultrasonicvibrations, according to an embodiment of the present invention;

[0060]FIG. 7 is a partial cross-section of coated optical fibres of theoptical channel plate of FIG. 2;

[0061]FIG. 8A is a transverse cross-section of an array of opticalfibres of the optical channel plate of FIG. 1;

[0062]FIG. 8B is a longitudinal cross-section of the array of FIG. 8A;

[0063]FIG. 8C-shows the array of FIG. 8A with a coating;

[0064]FIG. 8D-shows a longitudinal cross-section of the coated array ofFIG. 8C;

[0065]FIG. 8E-shows an optical channel plate formed from the array ofFIG. 8D;

[0066]FIG. 9A-shows a transverse cross-section of fibres used inmanufacture of a hollow optical waveguide channel plate of an embodimentof the present invention;

[0067]FIG. 9B-shows a longitudinal cross-section of the fibres of FIG.9A;

[0068]FIG. 9C-shows the array of FIG. 9A covered with a coating;

[0069]FIG. 9D-shows a longitudinal cross-section of the coated array ofFIG. 9C;

[0070]FIG. 9E-shows a longitudinal cross-section of a slice formed fromthe coated array of FIG. 9D;

[0071]FIG. 9F-shows a transverse cross-section of a hollow waveguidechannel plate formed from the slice of FIG. 9E after melting andremoving the fibre material;

[0072]FIG. 9G-shows a longitudinal cross-section of the hollow waveguidechannel plate of FIG. 9F;

[0073]FIG. 10-shows light rays reflected from the reflective opticalfibre channel plate of FIG. 8E;

[0074]FIG. 10A-shows light rays collimated and reflected from atransmission optical fibre channel plate of an embodiment of theinvention;

[0075]FIG. 11-shows light rays reflected from the hollow opticalwaveguide reflective optical channel plate of FIG. 9G;

[0076]FIG. 11A-shows light rays collimated and reflected from atransmission hollow optical waveguide channel plate of an embodiment ofthe invention;

[0077]FIG. 12-shows a cross-section of a concave optical channel platemirror according to the invention;

[0078]FIG. 13 & FIG. 14-show tapered optical fibres used in anembodiment of the present invention;

[0079]FIG. 15A-shows a flat display device using the tapered opticalfibres of FIGS. 13 & 14;

[0080]FIG. 15B-shows a cross-section of a line B-B of FIG. 15A;

[0081]FIG. 16-shows a trifurcated optical fibre for use in the presentinvention;

[0082]FIG. 17-shows an application of channel plates of the presentinvention for producing an image on a side of building, the image beingtransmitted from an opposed side of the building;

[0083]FIG. 18 is a perspective view of a machined block used in anembodiment of the invention for the production of an optical channelplate having hollow waveguides;

[0084]FIG. 19 is a top view of the machined block of FIG. 18;

[0085]FIG. 20 is a perspective view of a further machined block used inan embodiment of the invention for the production of an optical channelplate having solid waveguides;

[0086]FIG. 21 is a perspective view of cylinders machined from the blockof FIG. 20;

[0087]FIG. 22 is a top view of the cylinders of FIG. 21;

[0088]FIG. 23 is a perspective view of the cylinders of FIGS. 21 and 22embedded in support material;

[0089]FIG. 24 is a top view of the cylinders of FIG. 23;

[0090]FIG. 25 is a schematic view of a sheet of material and opposeddies used in an embodiment of the invention;

[0091]FIG. 26 is a schematic view of the sheet and dies of FIG. 25,showing the dies deforming the sheet to form a corrugated sheet;

[0092]FIG. 27 is a schematic view of a corrugated sheet of FIG. 26; and

[0093]FIG. 28 is a schematic view of a stack of corrugated sheets ofFIG. 27.

[0094] In the Figures like reference numerals denote like parts.

[0095] As shown in FIGS. 1 to 5, the optical channel plate of thepresent invention employs an array of aligned optical waveguides 10,11or 12 which in the case of hexagonal 11 or triangular 12 cross-sections,as best shown in transverse cross-section of FIGS. 1 and 3, are closelypacked with small interstitial spaces 115, 125 but are packed with largeinterstitial spaces 105 where the cross-section 10 of the waveguide iscircular as shown in FIG. 2.

[0096] In one embodiment of the invention the waveguides are opticalfibres. In order mutually to align the optical fibres 60 they may beassembled with their longitudinal axes horizontal and the optical fibresvibrated ultrasonically in the plane of their longitudinal axes in twomutually perpendicular directions, as indicated by double arrow headedlines 61,62 in FIG. 6, until the optical fibres fall into alignmentunder gravity. Alternatively, the optical fibres may be aligned by othermechanical means, for example, by centrifuging or under the influence ofgravity, preferably assisted by vibration of the fibres.

[0097] Referring to FIG. 7, before being aligned, the optical fibres 70may have an external coating 71 applied to their longitudinal surfacesto improve the internal optical reflectivity of the fibres.Alternatively, it will be apparent to those skilled in the art thatgraded index fibres could be used wherein the index of refraction of thematerial of the fibre changes along the radius of the fibre, to improvethe internal reflectivity.

[0098] The aligned optical fibres may then be adhered together bypassing adhesive into and through the interstitial spaces 105,115,125between the fibres. This is particularly appropriate in the case of, forexample, fibres 10 with circular cross-section shown in FIG. 2.Alternatively, using coated fibres 72, the fibres may be adheredtogether at touching portions of adjacent fibres by ultrasonicallyvibrating the fibres causing local melting of the coating at points ofcontact and, hence, welding together the fibres, or by heating thefibres by other means. Alternatively a heat-activated, or other,adhesive may be used.

[0099] Referring to FIG. 8, in a third method of manufacture accordingto the invention using an array of uncoated fibres 80, a coatingsolution may be passed through the interstitial spaces 84 to both form acoating 81 on the fibres and to bind the fibres 80 together in a bundle,see FIGS. 8C & 8D. In the interests of clarity of the figures the fibresare shown relatively further apart than they would be in practice. Sucha coating process may use known electroplating techniques. It will beapparent that the third method of manufacture could also be used withprecoated fibres and additional coating material could be used to bindthe fibres together.

[0100] In the case of closely packed bundles, some difficulty may beexperienced in passing either adhesives or coating solutions into theinterstitial spaces. The fibres may therefore, in such a case, beclamped together in a spaced apart configuration, as shown in FIGS. 8A &8B, rather than in their close packed configuration, shown in FIGS. 1 &3, to permit sufficient interstitial space for the passage of suchadhesive or coating solution. Alternatively, the fibres may be coatedafter they have been sliced into short lengths in a manner to bedescribed.

[0101] Once the array of optical fibres have been adhered togetherand/or coated in a bundle, the bundle is sliced into channel plates 82by cutting at an angle perpendicular to the axes of the fibres in amanner known per se. The end faces of the optical fibre optics arepolished. Where a reflective optical channel plate is required one ofthe end faces of the plate is then coated with a coating 83 ofreflective material.

[0102] Referring to FIGS. 9A-9G, in an alternative embodiment of theinvention, hollow optical waveguides 90 are used rather than opticalfibres 80. In this embodiment an array of fibres 93, not necessarilyoptical fibres, are formed as in the first embodiment. As in the firstembodiment, these fibres may be pre-coated or may be coated onceassembled into the array with a coating 92 as described in the firstembodiment. However, fibre material 93 is chosen which has a lowermelting point than the melting point of the coating 92 and subsequent toassembling the coated fibres and slicing the assembly into slices 95,the plates are heated sufficiently to melt the fibre to form moltenfibre material but to leave the coatings 92 unmelted. The molten fibrematerial is then removed from the slice to leave a honeycomb structureof hollow waveguides 90 formed by the coatings 92. It will beappreciated that the removal of the molten fibre material may beassisted by blowing through the honeycomb structure, where both ends ofthe channels are open. Alternatively, the removal of molten fibre can befacilitated by suction.

[0103] In the case of the production of reflective optical fibrechannels, one of the faces of the slice 95 is coated with a end coating96 before the fibres are melted so that a honeycomb structure is formedwith one end closed by optically reflective material.

[0104] A further embodiment of the invention is shown in FIGS. 18-24, inwhich an optical channel plate is machined from a block of material 180,200. In a first version of the embodiment as shown in FIGS. 18 and 19,an array of cylindrical bores 181 are drilled in the block 180 to formoptical waveguides through the block. A perspective view of the drilledblock is shown in FIG. 18 and a top view of the drilled block is shownin FIG. 19. In the interests of clarity the cylinders and distances areshown magnified in the figures, and only an exemplary number ofcylinders are shown. In practice the cylinders may be drilled at afrequency of up to 10,000 holes/inch (4,000 holes/cm) using, forexample, numerically controlled machining. The internal surfaces of thecylindrical bores may be coated with an optically reflective coatingafter drilling, so that the block of material 180 need not necessarilybe of optically reflective material.

[0105] Although the cylindrical bores are shown as right circularcylinders, it will be understood that any other cross-sectional shape,for example cylinders having a hexagonal cross-section, may be machinedinstead.

[0106] As in embodiments previously described, the block may be slicedtransversely to the axis of the cylinders, to provide a plurality ofoptical channel plates with hollow waveguides.

[0107] A second version of this embodiment is shown in FIGS. 20 to 24,in which material of the block 200 is machined away to leave an array ofsolid cylinders 201 of the block material, as shown in perspective viewin FIG. 21 and as an end view in FIG. 22. In this version of theembodiment the block 200 is therefore necessarily of opticallytransparent material. The cylinders may be coated to increase theinternal optical reflectivity of walls of the waveguides thus formed. Asshown in FIGS. 23 and 24 this coating, or other additional material, maybe introduced in the interstitial spaces between the cylinders to act asa mechanical support for the cylinders. As in the previously describedversion of this embodiment, the block 230 of cylinders embedded insupport material may then be sliced if required to form a plurality ofoptical channel plates with solid waveguides, or the block may be usedas a single optical channel plate. It will be understood that once againthe waveguides do not necessarily have a cylindrical cross-section butmay, for example, have a hexagonal cross-section.

[0108] A further embodiment of the invention is shown in FIGS. 25 to 28.In this embodiment a sheet of material 250 is passed in direction ofarrow-headed line 251 between a first die 252 and an opposed offsetsecond die 253. The first die and the second die 253 each have a workinghead in the shape of a half hexagon. The sheet 250 may be paused with asection of the sheet 251 between the dies, and the first die 252 movedin the direction of the arrow-headed line towards the sheet to deformthe sheet and the second die 253 moved in an opposed direction to thatof the first die towards the sheet to deform the sheet, in the directionof arrow headed line 255, but offset from the first die. In this manner,first and second opposed corrugations 261 and 262 of half-hexagonalshape are formed in the sheet 250. The dies are then withdrawn and thesheet stepped forward in the direction of arrow headed line 251 to forma second pair of corrugations adjacent to the first pair to form acorrugated sheet as shown in FIG. 27. Some thinning of the sheet willnecessarily occur during pressing and this is allowed for in theoriginal selection of the thickness of the supplied sheet.

[0109] Although the dies have been shown and described as having workingheads which are in the shape of half hexagons, it will be understoodthat differently shaped working heads may be used to form corrugationsof different shapes, for example, semicircular working heads may beused.

[0110] It will be apparent that the sheet 250 must be sufficientlyductile to be deformed into corrugations. In the case of a glass sheetthis ductility may be achieved by working the sheet at a temperatureabove room temperature at which the glass is ductile. Conveniently, thismay be done immediately after manufacture of the glass sheet before thesheet has cooled from the manufacturing process.

[0111] As an alternative to the discontinuous process described, inwhich the first and second dies 254, 255 move in a direction transverseto the plane of the sheet 250, a series of die heads may alternativelyeach be mounted on respective first and second offset drums (not shown)having respective axles parallel to the plane of the sheet so that thesheet is continuously passed between the respective drums such thatsuccessive die heads on each respective drum deform the sheet. It willbe apparent that some adaptation of the shape of the die heads may berequired to achieve the required corrugations in this case to allowcontinuous movement of the sheet between the respective drums.

[0112] A number of corrugated sheets formed in this manner may then bestacked one upon another as shown in FIG. 28 to define channelstherebetween having, in the case of half-hexagonal dies, a hexagonalcross-section. As shown in FIG. 28, a plurality of such sheets may bestacked one upon another to form an array of channels, in which thechannels in successive layers are offset from each other. The corrugatedsheets may be transported and/or stacked using numerically controlledmachinery.

[0113] Where the sheet 250 is of optically reflective material, thesechannels form hollow waveguides. Where the sheets are not of opticallyreflective material, or to increase the optical reflectivity, the innersurfaces of the channels may be coated with optically reflectivematerial to form hollow waveguides.

[0114] The stacked corrugated sheets may be adhered together at thepoints of contact by any known method, dependent on the material of thesheets 25, for example they may be welded together or adhesive may beused. Where the sheets are of glass at an elevated temperature thesheets may be pressed together as the glass cools so that the sheets aremelded together.

[0115] It will be appreciated that the blocks of waveguides so formedmay be transversely sliced if so desired to form a plurality of opticalchannel plates with hollow optical waveguides.

[0116] In one example of the embodiment the sheet of material is a metrewide in the direction transverse to the direction of motion shown byarrow headed line 251.

[0117] It will be appreciated that with suitable adaptation of theplacement and shape of the dies, an optical channel plate with solidwaveguides may be formed.

[0118] Referring to FIG. 10, for use as a front projection screen 100,or a front projection display, an image is projected from a projectoronto the uncoated or open ends of a reflective optical channel plate andthe light 101 from the projector is collimated by reflections 102 fromthe side walls 103 of the optical waveguides 104, non-specularlyreflected 105 from the end of the waveguides opposed to the end at whichthe light enters the waveguides and further collimated by furtherreflection 106 from the side walls 103 before emerging from the uncoatedend of the optical channel plate. A small portion 107 of the incidentlight 101 may be reflected from the uncoated end of the optical channelplate. However, in general, stray light 108 entering the waveguides atan angle greater than that at which the image enters will not bereflected back to a viewer to degrade the image. Some stray light 109may be reflected from the uncoated end face of the optical channel pate.In addition, the reflected light is collimated, so that a much largerproportion is reflected towards a viewer than would be in the case oflight scattered from a known screen without an optical channel plate. Itwill be evident that the invention, therefore, also has applicationwherever a high reflectively with collimation is required, for example,on vehicle reflectors or road signs. As shown in FIG. 11, the use of thehollow waveguides 111 overcomes the problem of reflection from the frontface of the channel plate which may be experienced with a reflectiveoptical channel using optical fibres. In this case incident stray light118 is largely absorbed by repeated reflections within the hollowwaveguide.

[0119] The reflective optical channel plate also has application in, forexample, large screen displays for reflecting images projected onto theside of a building.

[0120] Referring to FIG. 12, a further application of the reflectiveoptical channel plate is for the production of concave 120 or convexmirrors by forming a reflective channel plate into a required concave orconvex shape. Such optical channel mirrors, using specular reflections,have particular application in reflective telescopes for providing highreflectivity and reducing reflection of stray light.

[0121] It will be apparent that transmission optical channel plateslocated on a viewing side, or front, of a rear projection or phosphorscreen can similarly be used to reduce the effect of reflection of strayor ambient light from the front of the screen, to enhance the contrastof an image projected or produced on the rear of the screen, similarlyto the use of reflective optical channel plates illustrated in FIGS. 10and 11.

[0122] In the case of transmission optical fibre channel plates, asshown in FIG. 10A, a rear projection beam 101′ incident on a rearprojection or phosphor screen 1000 causes the scattering or emission oflight, respectively, from the screen so that light rays 1001 arecollimated by reflections 102′ from the side walls 103′ of the opticalwaveguides 104′ before emerging from an uncoated end of the opticalchannel plate. However, in general, stray light 108′ incident on aviewing side of the screen is weakly reflected 109′ from the surface ofthe waveguide but predominantly is refracted 1009 into the waveguide andabsorbed by repeated reflections so that stray light does not interferewith the image.

[0123] As shown in FIG. 11A, a hollow optical waveguide channeltransmission plate may be used without a scattering or phosphor screen.A rear projection beam 111′, such as a laser beam, is scattered byreflections 112′. Incident stray light 118′ on a viewing side of thescreen is, however, absorbed by repeated reflections within the hollowwaveguide, so as not to interfere with a viewed image produced by thelight rays 1101.

[0124] Transmission optical channel plates have particular applicationin association with flat displays. For example, by the use of taperedfibres 130, as shown in FIGS. 13 & 14, transmission optical channelplates can be used to produce an enlarged image by projecting an imageonto the small diameter ends of the tapered fibres to be emitted fromthe larger diameter end of the fibres. Such tapered fibres are known perse for use with displays from, for example, WO 97/38329 and FR 2628875in which the optical fibres are fabricated by drawing under gravity.

[0125] In a further application of the invention, waveguides may be usedto deliver an image to the rear of a display screen, as shown in aschematic representation in FIGS. 15A & 15B, which show onlyrepresentative examples of the optical fibres of the channel platearray. Such a transmission optical channel plate using taperedwaveguides, can be used to produced extremely high resolution displays.For example, mechanical or quartz light rotators may be used to deliverhorizontal or vertical scans to the input ends 151 of the opticalwaveguides 152. As shown in FIG. 15B, the optical waveguides can becurved so that the entry points of the fibres are more or less in aplane of the display screen 153 which they are illuminating. In thisway, substantially flat display devices may be produced.

[0126] Bending of the optical waveguides of a transmission opticalchannel plate can also be employed to produce lenses, for example, forthe concentration of solar radiation in a manner analogous to theproduction of a concave mirror shown in FIG. 12. A further applicationmay be in spectacle lenses.

[0127] In a similar manner, where the waveguides are of photoemissivematerial or are coated with photoemissive material, such channel platesmay be used in photomultipliers. In one embodiment, the waveguides, ifelectrically conductive, are electrically insulated from each other, forexample, by an insulating coating. If photons are incident on the wallsof a waveguide, electrons will be emitted from the walls. If the channelplate is subjected to an electric field the electrons may subsequentlybe accelerated towards and be incident on a phosphor screen to cause theemission of light.

[0128] As shown in FIG. 16, colour mixing of displays can also beimproved over known displays by passing coloured light from threeseparate light sources through single fibres 160 of an optical channelplate to be produced in a required colour 161 at an emission end 162 ofthe fibres. This, for example, may be done by optically coupling threefibres together into the input of the waveguide of a transmissionoptical channel plate, the three fibres being illuminated by threedifferently coloured light sources 163,164,165. This overcomes theproblem of colour separation frequently encountered with large screenback projection displays due to the physical separation, for example, ofphosphors on a screen for each of the three constituent colours. Becausein this way a coloured pixel is produced with a single pixel rather thanwith three differently coloured pixels as in the prior art, a 3:1increase in resolution of the screen is obtained.

[0129] Referring to FIG. 17, a further, large scale, application of thetransmission channel plates of the invention is the production of plateswhich bend around, or pass through a building 170 so that an input endof the plate covers, for example, one face 172 of the building and theoutput end of the plate covers an opposed face 173 of the building. Inthe interests of clarity of the figure, only representative examples ofthe optical waveguides of the channel plate array are shown in thefigure. In this manner, light received on one side of the building istransmitted to the opposed side of the building so that, if the inputand output of all the fibres are respectively aligned on either side ofthe building, an image of the view 174 as seen from one side of thebuilding is transmitted and displayed as an image 175 on the opposedside of the building, so that the building effectively becomesinvisible.

1. A method for forming a solid optical channel plate comprising thesteps of: a) providing optical fibres having respective longitudinalaxes in side-by-side relationship; b) using mechanical aligning means toalign the optical fibres in a two dimensional array with the respectivelongitudinal axes substantially parallel, to form a substantiallyregular geometric pattern in cross-section; c) adhering the opticalfibres together along at least a portion of their longitudinal surfaces;and d) transversely slicing the array of optical fibres to form at leastone optical channel plate.
 2. A method as claimed in claim 1, whereinthe step of providing optical fibres in side-by-side relationshipincludes heating and pulling the optical fibres to form tapering fibres.3. A method as claimed in claims 1 or 2, wherein the step of providingoptical fibres in side-by-side relationship includes the step of coatingthe optical fibres with coatings along longitudinal surfaces of theoptical fibres to increase internal optical reflectivity of the opticalfibres.
 4. A method as claimed in claim 3, wherein the step of coatingthe optical fibres includes coating by electroplating.
 5. A method asclaimed in any of the preceding claims, wherein the step of aligning theoptical fibres with mechanical means includes the step of aligning theoptical fibres with ultrasonic vibrating means.
 6. A method as claimedin claims 3 or 4, wherein the step of adhering the optical fibresincludes ultrasonically vibrating the optical fibres such that portionsof the coatings of adjacent optical fibres are heated and weldedtogether.
 7. A method as claimed in any of the preceding claims, whereinthe step of the adhering the optical fibres comprises using adhesive. 8.A method as claimed in any of the preceding claims, wherein the step oftransversely slicing the array to form at least one optical channelplate includes the further step, after slicing the array, of polishingat least one of the opposed end surfaces of the optical fibres, whichtogether form opposed end surfaces of the at least one optical channelplate.
 9. A method as claimed in claim 8, wherein the step of polishingthe at least one of the opposed end surfaces of the at least one opticalchannel plate includes coating one of the end surfaces of the at leastone optical channel plate to increase the internal optical reflectivityof the respective end surfaces of the at least one optical channelplate, to form at least one reflective solid optical channel plate. 10.A method as claimed in any of the preceding claims, wherein the step ofproviding optical fibres in side-by-side relationship includes providingoptical fibres having a circular transverse cross-section.
 11. A methodas claimed in any of claims 1 to 9, wherein the step of providingoptical fibres in side-by-side relationship includes providing opticalfibres having a polygonal, preferably hexagonal, transversecross-section.
 12. A method of forming a honeycombed optical channelplate comprising the steps of; a) providing an array of aligned coatedfibres, the fibres having optically reflective coatings with a meltingpoint higher than that of the fibres; b) transversely slicing the arrayof coated fibres to form at least one plate of coated fibres; c) heatingthe at least one plate of coated fibres to melt the fibres to formmolten fibre material; and d) removing the molten fibre material fromthe at least one plate of coated fibres to leave the opticallyreflective coatings as hollow optical waveguides forming a honeycombedoptical channel plate.
 13. A method as claimed in claim 12, wherein thestep a) of providing an array of aligned coated fibres includes thesteps of providing an array of aligned fibres longitudinally spacedapart by longitudinal interstitial spaces; and passing coating solutionbetween the aligned, spaced apart, fibres to fill the interstitialspaces and thereby coat the fibres along their lengths to form an arrayof coated fibres having optically reflective coatings with a meltingpoint higher than that of the fibres, such that the optically reflectivecoatings cause the fibres to adhere together along their lengths.
 14. Amethod as claimed in claim 12 or 13, wherein the step of providing anarray of aligned coated fibres includes the step of aligning the fibresusing ultrasonic vibrating means.
 15. A method as claimed in any ofclaims 12 to 14, wherein the step of providing an array includes heatingand pulling the fibres to formed tapering fibres.
 16. A method asclaimed in any of claims 12 to 15, wherein the fibres are coated byelectroplating.
 17. A method as claimed in any of claims 12 to 16,wherein the step of providing an array of aligned fibres includesproviding fibres having a circular transverse cross-section.
 18. Amethod as claimed in any of claims 12 to 16, wherein the step ofproviding an array of aligned fibres includes providing fibres having apolygonal, preferably hexagonal, transverse cross-section.
 19. A methodas claimed in any of claims 12 to 18, wherein the step of slicing thearray to form at least one plate includes coating a major face of the atleast one plate with an optically reflective end coating, such that thestep of removing the molten fibre material from the at least one plateleaves the optically reflective coatings as hollow optical waveguidesclosed at one end by the optically reflective end coating, to form areflective honeycombed optical channel plate.
 20. A method for formingan optical channel plate comprising the steps of: a) providing an arrayof aligned optical waveguides interconnected in side-by-siderelationship spaced apart by interstitial spaces; b) clamping theoptical waveguides in position with respect to each other to formclamped optical waveguides; c) transversely slicing the array ofwaveguides to form at least one clamped optical waveguide plate withinterstitial spaces; d) filling the interstitial spaces in the waveguideplate with optically reflective coating material to improve the internaloptical reflectivity of the waveguides and to adhere the waveguidestogether in the array; and e) unclamping the clamped optical waveguideplate to form an optical channel plate.
 21. A method as claimed in claim20, wherein the step of providing an array of aligned optical waveguidesincludes using ultrasonic vibrating means to align the opticalwaveguides.
 22. A method of forming an optical channel plate comprisingsubstantially parallel hollow optical waveguides, the method comprisingthe steps of: a) providing a plurality of corrugated sheets of opticallyreflective material; b) stacking the plurality of corrugated sheets oneupon another to form substantially parallel spaced apart opticalwaveguides between adjacent stacked sheets; and c) adhering adjacentsheets to each other.
 23. A method as claimed in claim 22, wherein thestep of providing a plurality of corrugated sheets of opticallyreflective material includes the step of coating sheets of non-opticallyreflective material with an optically reflective coating.
 24. A methodas claimed in claim 22 or 23, wherein the step of providing a pluralityof corrugated sheets includes the step of forming corrugated sheets fromsubstantially plane sheets by using pressing means to deform thesubstantially plane sheets into corrugated sheets while the sheets arein a ductile state.
 25. A method as claimed in claim 22 to 24, whereinthe step of adhering adjacent sheets together includes the further stepof transversely slicing the adhered sheets into separate channel plates.26. A method of forming an optical channel plate comprisingsubstantially parallel optical waveguides comprising the steps of: a)providing a block of material; and b) machining the block to formsubstantially parallel optical waveguides therein.
 27. A method asclaimed in claim 26, wherein the step of providing a block of materialcomprises providing a block of optically reflective material.
 28. Amethod as claimed in claim 26 or 27, wherein the step of machining theblock includes the further step of coating the substantially paralleloptical waveguides with optically reflective material to increase theinternal optical reflectivity of the optical waveguides.
 29. A method asclaimed in any of claims 26 to 28, wherein the step of machining theblock to form substantially parallel optical waveguides thereincomprises forming solid optical waveguides of the material of the block.30. A method as claimed in any of claims 26 to 28, wherein the step ofmachining the block to form substantially parallel optical waveguidestherein comprises forming hollow optical waveguides within the materialof the block.
 31. A method as claimed in any of claims 26 to 30, whereinthe step of machining the block to form substantially parallel opticalwaveguides therein comprises machining under numerical control.
 32. Areflective optical channel plate for a front projection screen, theoptical channel plate comprising a plurality of optical waveguidesarranged in an array for location substantially perpendicular to a majorplane of the screen such that light of a projected image entering firstends of the optical waveguides is collimated by the optical waveguidesand reflected from opposed second ends of the optical waveguidesrespectively to be viewed after reflection with substantially nointerference from stray light reflected from the second ends of thewaveguides.
 33. A reflective optical channel plate as claimed in claim32, wherein the optical waveguides are optical fibres.
 34. A reflectiveoptical channel plate as claimed in claim 33, wherein the optical fibresare coated along their lengths to increase internal reflectivity of theoptical fibres.
 35. A reflective optical channel plate as claimed in anyof claims 32 to 34, wherein the optical waveguides are adhered togetheralong their lengths.
 36. A reflective optical channel plate as claimedin any of claims 32 to 35, wherein the second ends of the optical fibresare coated to increase internal reflectivity of the second ends.
 37. Areflective optical channel plate as claimed in claim 32, wherein theoptical waveguides are hollow optical waveguides.
 38. A reflectiveoptical channel plate as claimed in claim 37, wherein the array ofhollow waveguides has a honeycomb structure in transverse cross-section.39. A reflective optical channel plate as claimed in any of claims 32 to38, wherein the optical waveguides have a circular transversecross-section.
 40. A reflective optical channel plate as claimed in anyof claims 32 to 38, wherein the optical waveguides have a polygonal,preferably hexagonal, transverse cross-section.
 41. A reflective channelplate as claimed in any of claims 32 to 40, for a reflective telescope,wherein the channel plate is arcuate in a plane substantiallyperpendicular to the axes of the optical waveguides such that thechannel plate forms a collimated convex or concave mirror.
 42. Atransmission optical channel plate for a display screen, the opticalchannel plate comprising a plurality of optical waveguides forarrangement in an array substantially perpendicular to a major plane ofthe screen such that light of an image entering first ends of theoptical waveguides is collimated and transmitted from opposed ends ofthe optical waveguides respectively.
 43. A transmission optical channelplate as claimed in claim 42, wherein the optical waveguides taper fromthe screen to produce a magnified image on the screen and longitudinalaxes of the waveguides are at least partially arcuate such that lightmay enter ends of the waveguides at an angle substantially within theplane the screen to form a substantially flat display device.
 44. Atransmission optical channel plate as claimed in claims 42 or 43,wherein the optical waveguides trifurcate into three optically connectedsub-waveguides respectively such that light of different coloursentering from each of the sub-waveguides respectively may be combined ineach of the waveguides to illuminate a pixel on the screen,respectively.
 45. A transmission optical channel plate as claimed in anyof claims to 42 to 44, for a photomultiplier wherein the innerlongitudinal surfaces of the waveguides are coated with photoelectricmaterial, for the emission of electrons.
 46. A transmission opticalchannel plated as claimed in claim 45, wherein the axes of the opticalwaveguides are arcuate to increase the number of optical reflectionsfrom the coated inner longitudinal surfaces.